Method of constructing a dimension-



United States Patent Office 3,123,892 Patented Mar. 10, 1964 3,123,892 ME'EHQD @F C'GNSTRUCTENG A DlMENSlGN- ALLY STABLE DRYER FELT Henry J. Mach Kilian, Delmar, and Robert R. Kelleher, Lathazn, FLY assignors to Albany Felt Company, Albany, N.Y., a corporation of New York No Drawing. Filed Sept. 21, 1960, Ser. No. 57,398 3 Claims. (Cl. 2tl-72.2)

This invention relates generally to paperm akers felts and more particularly to such a felt which is provided to be used on the dryer section of a papermaking machine and which is commonly referred to as a dryer fel-t.

Dryer felts are used in papermaking to hold the sheet of paper which is being produced in contact with the heated dryer cylinders of the papermaking machine as the paper travels through the drying section of the machine. Dryer felts are either made in endless form or have their ends joined together by some means to produce an endless belt.

The felts used in the drying section of the papermakin-g machine differ appreciably from the felts used in the wet section of the papermaking machine in that the dryer felts must exhibit a higher degree of stability during operation over both long and short periods.

Dryer felts in use today are for the most part woven fabrics produced from yarns of cotton, wool, asbestos, synthetic fibers, or combinations of these materials. Various weaves are used to provide varying degrees of permeability and surface smoothness. Often, in attempting to obtain a smooth surface by finer construction, permeability must be sacrificed. Conversely, in designing a dryer felt for permeability, the surface may not result in as smooth a characteristic as required for the grade of paper being dried. In the situations where dryer felts have been made of synthetic fibers, exposure to the heat of the dryers has frequently caused an undesirable dimensional change rendering the felt unsatisfactory for use.

The invention herein seeks to overcome the difficulties presently encountered in the production of dryer felts by providing a method of producing a stable dryer felt comprised of a central structure of woven fabric of sufficiently coarse yarns to provide the necessary strength, and a surface structure, non-woven in character, attached to the central structure by a needling operation.

The invention herein disclosed, therefore, has as its principal object the furnishing of a dimensionally stable felt with a synthetic surface for the dryer section of a pepermaking machine.

Another object of this invention is to provide a dimensionally stable dryer felt which because of its smooth surface characteristic will not mark the paper but one which will be highly permeable.

A further object of this invention is to provide a dryer felt which will be dimensionally stable over long as well as short periods of use and one which will remain clean over long periods of use.

A further object of this invention is to provide an improved endless dryer felt which has no sea-m.

Still another object of this invention is to provide a dryer felt of synthetic fibers which is stable against dimensional change under operating conditions thereby making it possible to obtain the extended life in a dryer felt made available by certain of the synthetic fibers available today without undesirable dimensional changes.

The base or central stnucture of the felt is preferably a fabric woven endless so that the 100111 warp becomes the crosswise yarn in the finished fabric and the loom filling becomes the lengthwise yarn in the finished fabric. The central fabric need not be woven endless although that form is desirable. The fabric should be woven relatively coarse to give a high degree of permeability. However,

the specific weave utilized can vary with the particular application and is not critical.

The yarns from which the base fabric is woven are selected to give the base fabric stability, strength, ease of weaving, long life and ability to resist degradation due to heat and use, and the ability to allow water vapor to pass therethrough. The material from which'the base fabric is woven and the weave itself must be selected with this in mind.

In its preferred form the base fabric of the dryer felt which is the subject of this invention is woven of yarns formed from a synthetic fiber-forming material such as Dacron polyester (Dacron is a registered trademark of Du Pont Company, USA.) or a Kodel polyester (Kodel is a registered trademark of Eastman Chemical Products, U.S.A.). The yarns are selected primarily to achieve the result required and therefore yarns possessing desirable performance qualities which are natural yarns or yarns which are a blend of natural and synthetic fibers can be used.

The yarns in the base fabric are preferably three-ply and five-ply. With such yarns it has been found that the base fabric will handle well in subsequent processing and have the desired characteristics when finally utilized. Toward this end, three-ply lengthwise yarns of 1800 grains per yards have been utilized. Singles twist were put in at 918 right in 72 inches. The three-ply twist put in was 218 left in 72 inches. The crosswise yarns were fiveply, 1000 grains per 100 yarns. The singles twist put in was 652 right in 72 inches and the ply twist put in. was 324 left. In both cases with twists outlined as above, the yarns are all synthetic.

Depending upon the Weight of ultimate felt desired, normally the base fabric is woven with aplain weave. For increased bulk other weaves could be substituted. The yarn sizes could be modified to change the weight or ounces per square foot of the base fabric.

After the base fabric has been woven, the material is run as an endless belt at elevated temperatures between 300 to 400 F. to stretch the material to between 10 to 20% or, as an optimum, about 14%. This likewise reduces the width about the same percentage. The lower temperature of 300 F. is selected since this is above the normal operating temperature of a dryer felt. The heat stabilization takes place at a tension of 25 pounds per inch of width, allowing the width to contract unrestricted. For certain application a tension Within the range 20 to 30 pounds per inch of width may be found acceptable.

After the base fabric has been woven and stabilized as set forth above, a plurality of surface fibers are mechanically locked thereto by a needling operation. The base fabric is passed through the needling machine and fibers applied to both sides until the desired weight blanket has been achieved. This surface structure makes up a sufficient proportion of the total weight, in the range of 40 to 60% and preferably 46% as an example, so that it adequately covers the central woven fabric and provides a smooth surface. The penetration or the distance that the needle goes through the material during needling can be changed according to the characteristics desired.

The needle is selected with the end use in mind and the penetration of the needle depends on the type of needle. Change in the needle will affect the strength and the surface characteristic.

The web fibers, or fibers which are interlocked with the base fabric in the needling machine, can be synthetic fibers, such as polyester fibers of the type from which the base fabric is formed, or other synthetic fibers or natural fibers, or a combination of natural and synthetically formed fibers. The fibers selected are laid on the base fabric just prior to passing it through the neediing machine.

In the preferred embodiment needling was accomplished by putting two layers of a .34 ounce per square foot web of regular Dacron on the back side. For each penetration of the needle the fabric was advanced approximately .14 inch and the needle penetrated the fabric .587 inch. The fabric was then turned over and three layers of the same weight of material were placed on the other side of the material. The material was again turned and two additional layers of the same weight of material were placed on the back side of the fabric. The felt length is maintained during the needling operation.

After the needling has been completed the material is washed and subsequently dried under tension at elevated temperature substantially the same as before so that an additional stabilization takes place. The tension and temperature are selected according to the conditions which the dryer felt will encounter when in use so that the conditions in the stabilization process are more extreme than the normal conditions to be encountered in operation.

The high permeability of the felts made according to this invention results first from the fact that the central fabric is relatively coarse and so has good sized openings between yarns and, second, from the fact that the fibers of the surface structure where they pass through the central fabric lie predominantly in a direction perpendicular to the plane of the felt, thereby providing a multiplicity of capillary openings not found in a typical woven dryer felt.

Because it is possible to weave the central fabric in endless form, and to carry out the needling operations on that endless form, dryer felts which are truly endless without a seam or join of any kind can be produced by this method.

The degree of stabilization of dimension achieved is such that dryer felts made of Dacron base and web by this process change in dimension in operation less than one percent in length and less than two percent in width.

Thus, among others, the several objects in the invention as specifically aforenoted, are achieved. Obviously, numerous changes in construction and rearrangement of steps in the method might be resorted to without departring from the spirit of the invention as defined by the claims.

We claim:

1. The method of constructing a felt for use in the dryer section of a papermaking machine consisting of weaving a coarse base fabric with three-ply lengthwise yarns and five-ply crosswise yarns, running the base fabric as an endless belt at elevated temperatures in the range of 300 to 400 F. while applying tension in the range of 20 to 30 lbs. per inch of width, applying selected fibers to one surface of the base fabric and passing the base fabric through a needling machine to cover the surface of the Woven fabric with a plurality of fibers mechanically interlocked therewith, applying selected fibers to the remaining surface of the base fabric and passing the base fabric through a needling machine to cover the remaining surface of the woven fabric with a plurality of fibers mechanically interlocked therewith, repeating the application of fibers and needling until the fibers form 40 to of the total Weight of the resultant fabric and then washing and drying the fabric at elevated temperatures in the range of 300 to 400 F. while applying tension in the range of 20 to 30 lbs. per inch of width.

2. The method of constructing a felt for use in the dryer section of a papermaking machine in accordance with claim 1 in which the yarns from which the base fabric is woven and the plurality of fibers interlocked with the base fabric during the needling operations are formed from a polyester fiber-forming material.

3. The method of constructing a felt for use in the dryer section of a papennaking machine in accordance With claim 1 in which the length of the base fabric is maintained during the needling operations.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF CONSTRUCTING A FELT FOR USE IN THE DRYER SECTION OF A PAPERMAKING MACHINE CONSISTING OF WEAVING A COARSE BASE FABRIC WITH THREE-PLY LENGTHWISE YARNS AND FIVE-PLY CROSSWISE YARNS, RUNNING THE BASE FABRIC AS AN ENDLESS BELT AT ELEVATED TEMPERATURES IN THE RANGE OF 300* TO 400*F. WHILE APPLYING TENSION IN THE RANGE OF 20 TO 30 LBS. PER INCH OF WIDTH, APPLYING SELECTED FIBERS TO ONE SURFACE OF THE BASE FABRIC AND PASSING THE BASE FABRIC THROUGH A NEEDLING MACHINE TO COVER THE SURFACE OF THE WOVEN FABRIC WITH A PLURALITY OF FIBERS MECHANICALLY INTERLOCKED THEREWITH, APPLYING SELECTED FIBERS TO THE REMAINING SURFACE OF THE BASE FABRIC AND PASSING THE BASE FABRIC THROUGH A NEEDLING MACHINE TO COVER THE REMAINING SURFACE OF THE WOVEN FABRIC WITH A PLURALITY OF FIBERS MECHANICALLY INTERLOCKED THEREWITH, REPEATING THE APPLICATION OF FIBERS AND NEEDLING UNTIL THE FIBERS FORM 40 TO 60% OF THE TOTAL WEIGHT OF THE RESULTANT FABRIC AND THEN WASHING AND DRYING THE FABRIC AT ELEVATED TEMPERATURES IN THE RANGE OF 300* TO 400*F. WHILE APPLYING TENSION IN THE RANGE OF 20 TO 30 LBS. PER INCH OF WIDTH. 